Power systems, particularly internal combustion engines like diesel engines, gasoline engines and natural gas burning turbines, create a number of byproducts and emissions during operation including nitrogen oxide emissions such as NO and NO2, sometimes represented as NOX. In response to increased government-mandated regulations over such emissions, manufacturers of internal combustion engines have developed measures to reduce the amount or effect of the nitrogen oxides produced by the internal combustion process. One method is a chemical process called selective catalytic reduction, which may be referred to as SCR. In the SCR process, a gaseous or liquid reductant agent is introduced to the exhaust system where the reductant agent can intermix with the exhaust gasses or it can be adsorbed onto a catalyst located in the exhaust system downstream of the internal combustion engine. A common reductant agent is urea, though other suitable substances such as ammonia may be readily used in the SCR process. The NOx pollutants can react with the reductant agent and the catalyst such that the NOx is converted into nitrogen (N2) and water (H2O).
The catalyst used in the SCR process may include an internal support structure or substrate matrix that has been treated or coated with an active material that promotes the SCR conversion process. For example, the matrix may be metal or ceramic or a combination like copper zeolite coated with a base metal like vanadium. In a large scale application, multiple catalysts may be disposed in a common housing or module, such as indicated in U.S. Patent Publication No. 2009/0113709 titled “Method of Manufacturing Exhaust Aftertreatment Devices,” herein incorporated by reference in its entirety. That application describes a plurality of monolithic substrates that may be wrapped in a support mat and inserted via a soft-stuffing process into a cylindrical housing for retention.
Over time, the active material in SCR catalysts may become depleted or may become deactivated due to other products in the exhaust gasses such as phosphorous or sulfur collecting in the catalyst. Additionally, the substrate matrix is commonly designed as a thin-walled grid or frame that may become damaged. Accordingly, it may be necessary to occasionally remove the SCR catalysts from the exhaust system for repair or replacement. However, where multiple catalysts are included in a housing or module, especially in exhaust systems associated with large power systems, removal and replacement of an individual catalyst may be complicated.